This invention relates to compositions for the photogeneration of acid. This invention also relates to processes for the photogeneration of acid.
Many processes are known using a medium which, when irradiated with electromagnetic radiation, generates an acid. This acid is then used to cause a change in the properties of the medium, so that exposed and unexposed portions of the medium differ in their properties. For example, many photoresist compositions are of this type; the acid produced upon exposure to (typically) ultraviolet radiation changes the solubility of the photoresist composition in the solution used to develop the photoresist. In most conventional acid-generating photoresist processes, the sensitivity of the medium to the exposing radiation is not of major concern. Exposure is normally effected using powerful ultraviolet sources. In addition, long exposures times can usually be tolerated.
Today, many imaging processes are being developed using near infrared radiation from semiconductor diode lasers. Semiconductor diode lasers have the advantage of being much less expensive than ultraviolet lasers. They are also well adapted for the production of high resolution images and for digital imaging processes (i.e., for producing hard copies of images stored on computers in digital form). The cost per unit intensity is less for an infrared producing high-resolution addressable source than for a comparable ultraviolet radiation producing source. The imaging speed of such infrared radiation using processes is presently limited by the sensitivity of the medium, and accordingly, there is a need to develop infrared sensitive imaging media with improved sensitivity.
Oftentimes, the sensitivity of photosensitive compositions can be increased if the photosensitive molecule catalyzes a secondary reaction which is not radiation-dependent, and if the photosensitive molecule also effects conversion of several molecules for each quantum of electromagnetic energy absorbed. For example, photoresist systems are known in which the primary photochemical reaction produces an acid, and this acid is employed to eliminate acid-labile groups in a secondary, radiation-independent reaction. See, for example, U.S. Pat. Nos. 3,923,514 and 3,915,706. Also, U.S. Pat. No. 5,084,371 discloses a radiation-sensitive mixture which contains a water-insoluble binder comprising a mixture of phenolic and novolak polymers soluble or dispersible in aqueous alkali, and an organic compound whose solubility in alkaline developer is increased by acid, and which also contains at least one acid-cleavable group, and in addition a further group which produces a strong acid upon exposure to radiation. A secondary acid generator (when used) xe2x80x9camplifiesxe2x80x9d the acid produced by an iodonium salt or other superacid precursor, resulting in several molecules of acid being produced for each molecule of superacid originally produced by decomposition of the iodonium salt. However, despite the increase in sensitivity achieved by such acid amplification, the contrast, and hence the quality of the resultant image is still governed by the original photochemical acid generation step. Accordingly, it is desirable to secure as high a quantum yield as possible during the photochemical acid generation step.
U.S. Pat. No. 5,286,604 discloses the use of a squarylium dye as a near infrared (NIR) light-to-heat converter for the thermal cleavage of tetrahydropyran groups from derivatized polyacrylate and methacrylate polymers for application in color proofing materials. However, the sensitivity of this system is quite low, i.e., 300-600 mJ/cm2. There is no disclosure of a squarylium dye used as a spectral sensitizer for latent Bronsted acid generators.
U.S. Pat. No. 5,225,316 discloses the use of various classes of dyes including, but not limited to, aryl nitrones, xanthenes, anthraquinones, substituted-diaryl and triaryl methanes, methines, merocyanines, and polymethines, thiazoles, substituted- and unsubstituted-polycyclic aromatic hydrocarbons, and pyrylium dyes in combination with iodonium salts for the photochemical imagewise generation of acid to cleave tetrahydropyran groups from derivatized polyacrylate and methacrylate polymers for application in no-process printing plates. However no mention was made specifically of squarylium dyes.
European Patent Publ. No. 568,993 discloses combinations of squarylium dyes and latent Bronsted acid generators (iodonium salts, trichloromethyl-substituted triazines, etc.) for the generation of acid by exposure to visible and NIR light. The acid that is generated catalyzes various imaging mechanisms including thermal crosslinking and thermal deprotection of hydrolyzable groups from polymers. Several examples describe the thermal crosslinking of phenolic resins and melamine formaldehyde resins catalyzed by acid photogenerated by combinations of squarylium dyes and tris(trichloromethyl-s-triazine). None of the squarylium dyes disclosed contain a 2,3-dihydroperimidine terminal group.
U.S. Pat. No. 5,340,699 discloses the use of NIR squarylium dyes in combination with latent Bronsted acid generators such as diphenyliodonium salts or trichloromethyl-containing molecules to generate a strong Bronsted acid which is used to catalyze the thermal crosslinking ,of a combination of novolak resin and resole resin.
U.S. Pat. No. 5,401,607 discloses an acid-generating medium comprising an iodonium salt and a squarylium dye in which the squarylium dye absorbs in the range of 700-1200 nm. The squarylium dye preferably has an oxidation potential in methylene chloride of not greater than 500 mV relative to the saturated calomel electrode (SCE). This patent teaches that dyes having oxidation potentials greater than about 500 mV were found not to be good acid generators.
U.S. Pat. No. 4,554,238 discloses the use of sensitizing dyes in the range 300-900 nm as electron donor sensitizers of nitrobenzyl-blocked surfactants to release the Bronsted acid form of the surfactant. The patent states that spectral sensitizing compounds suitable for the invention include those disclosed in the art as being suitable for the spectral sensitization of photolyzable organic halogen compounds (including trichloromethyl-substituted triazines), and sulfonium and iodonium salts. NIR squarylium dyes are disclosed, but there is no teaching that squarylium dyes can sensitize latent Bronsted acid generators.
K. A. Bello, S. N. Corns and J. Griffiths, J. Chem. Soc., Chem. Commun., 452-454, 1993 describes the condensation of 2,3-dihydroperimidines with squaric acid to give squarylium dyes having absorption maxima near 800 nm.
In one embodiment, the present invention provides an acid-generating medium comprising:
(a) a photochemical acid progenitor; and
(b) a squarylium dye having a; nucleus of the general formula: 
wherein:
R1 to R4 are independently selected from hydrogen, alkyl, cycloalkyl, aralkyl, carboalkoxyalkyl and carboaryloxyalkyl groups;
X represents  greater than CR5R6,  greater than POR7, or  greater than BOR7 
wherein:
R5 and R6 are independently selected from hydrogen, alkyl, cycloalkyl, aryl, and aralkyl groups;
or R1 and R5, and/or R2 and R6, and/or R3 and R5, and/or R4 and R6, and/or R5 and R6 represent the necessary atoms to complete a 5-, 6- or 7-membered ring; and
R7 represents an alkyl group.
It will be readily appreciated that the dyes of formula (I) may be represented by a number of different resonance structures, reflecting the many different ways in which the delocalized xcfx80-electron system may be visualized and notated. In formula (I) and elsewhere in this specification, the moiety: 
represents the aromatic dication derived from cyclobutadiene. This particular notation is chosen for convenience, and allows both the end groups and the central portion of the dye molecule to be depicted in full aromatized form. It must be emphasized, however, that formula (I) is to be interpreted as including all the possible resonance forms, such as: 
and the like.
In another embodiment, this invention provides an acid generating medium comprising:
(a) a photochemical acid progenitor selected from the group consisting of diaryliodonium salts, aryldiazonium salts, and 1,3,5-tris(trichloromethyl)-s-triazines; and
(b) a squarylium dye having an oxidation potential in dichioromethane greater than or equal to 0.5 V and less than or equal to 0.8 V relative to a standard calomel electrode.
This invention also provides a process for generating acid, comprising the steps of:
(a) providing a mixture of a photochemical acid progenitor and a squarylium dye of the formula (I) disclosed earlier herein; and
(b) irradiating the mixture with radiation from a light source, preferably a laser emitting in the near infrared region (700 to 1200 nm) of the spectrum.
It is generally accepted in the field of the present invention to allow substantial substitution on the core dye structure of the present invention. Some types of substitution, especially that which improves solubility in a selected solvent, is particularly desirable. Where the term xe2x80x9cgroupxe2x80x9d or xe2x80x9ccentral nucleusxe2x80x9d is used in describing an aspect of the present invention, that term implies that any type of substitution is acceptable, as long as the basic structure is maintained. For example, xe2x80x9calkyl groupxe2x80x9d would include not only standard hydrocarbon alkyls such as methyl, ethyl, cyclohexyl, isooctyl, undecyl, etc., but would also include substituted-alkyl such as hydroxymethyl, omega-cyanopropyl, 1,2,3-trichlorohexyl, 1-carboxy-iso-octyl, phenyldecyl, and the like. The term xe2x80x9calkylxe2x80x9d or xe2x80x9calkyl moietyxe2x80x9d indicates that there is no substitution on that defined component.
Other aspects, advantages, and benefits of the present invention are apparent from the detailed description, examples, and claims.
Squarylium dyes of the present invention have a nucleus of the general formula: 
wherein:
R1 to R4 are independently selected from hydrogen, alkyl, cycloalkyl, aralkyl, carboalkoxyalkyl and carboaryloxyalkyl groups;
X represents  greater than CR5R6,  greater than POR7, or  greater than BOR7 
wherein:
R5 and R6 are independently selected from hydrogen, alkyl, cycloalkyl, aryl, and aralkyl groups;
or R1 and R5, and/or R2 and R6, and/or R3 and R5, and/or R4 and R6, and/or R5 and R6 represent the necessary atoms to complete a 5-, 6- or 7-membered ring; and
R7 represents an alkyl group.
Preferably, R1 to R4 are independently selected from hydrogen; a substituted or unsubstituted alkyl or cycloalkyl group having from 1 to 20 carbon atoms; an aralkyl group having from 6 to 20 carbon atoms such as benzyl or p-dodecylbenzyl; a carboalkoxyalkyl group with the alkoxy group having from 1 to 20 carbon atoms such as carboethoxymethyl or carbooctyloxymethyl; and a carboaryloxyalkyl group with the aryloxy group having from 5-20 carbon atoms such as carbo(p-dodecylphenoxy)methyl. Dyes in which one or more of R1 to R4 are other than hydrogen show enhanced solubility in organic solvents such as methylethylketone and 1-methoxy-2-propanol.
Preferably, R5 and R6 are independently selected from hydrogen; an alkyl or cycloalkyl group having from 1 to 20 carbon atoms; and a substituted or unsubstituted aryl group having from 5 to 20 carbon atoms. Examples of preferred groups from which R5 and R6 may be selected include xe2x80x94CH2OH, xe2x80x94CH2OR8, xe2x80x94CH2OCH2CO2R8, xe2x80x94CH2OC(xe2x95x90O)R8, xe2x80x94CH2OSO2R9, and xe2x80x94CH2OSi(R9)3, wherein R8 is independently an alkyl, alkaryl, aralkyl or aryl group and R9 is independently an alkyl or alkaryl group. In addition, R5 anand R6 taken together may form a 5- to 7-membered nucleus (e.g., heterocyclic, carbocyclic, etc.).
R1 and R5, and/or R2 and R6, and/or R3 and R5, and/or R4 and R6, and/or R5 and R6 taken together may represent the necessary atoms to complete a 5-, 6- or 7-membered ring. One example of the above situation would be where R1 and R5, and/or R3 and R5 are taken together to form a lactam group; R6 is an alkyl or aryl group; and R2 and R4 are hydrogen.
Preferably, R7 represents an alkyl group having from 1 to 20 carbon atoms.
Preferably, R8 is independently selected from an alkyl, alkaryl, aralkyl or aryl group having from 1 to 20 carbon atoms.
Preferably, R9 is independently an alkyl or alkaryl group having from 1 to 20 carbon atoms.
Squarylium dyes used in the present invention can be made according to procedures disclosed later herein, as well as those disclosed in U.S. Pat. Nos. 5,360,694 and 5,380,635.
Conventional photochemical acid progenitors (hereinafter known as acid progenitors) well-known in the art can be used in the present invention. Non-limiting examples include s-triazine compounds substituted with at least one trihalomethyl group such as 2,4,6-tris(trichloromethyl)-s-triazine, 2-(4-methoxyphenyl)-4,6-bis-(trichloromethyl)-s-triazine, 2-(4-methoxy-1-naphthalenyl)-4,6-bis(trichloromethyl)-s-triazine and the like, iron-arene complexes such as (xcex76-isopropylbenzene)(xcex75-cyclopentadienyl) iron (II) hexafluorophosphate, (xcex76-xylenes) (xcex75-cyclopentadienyl) iron (II) hexafluoroantimonate and the like, and onium salts such as diaryliodonium salts, triarylsulfonium salts, triarylselenonium salts, dialkylphenacylsulfonium salts, dialkyl-4-hydroxyphenylsulfonium salts, aryldiazonium salts, nitrobenzyl esters such as p-toluenesulfonic acid ester of p-nitrobenzyl alcohol and the like, sulfonic acid esters such as p-hydroxymethylbenzoinsulfonic acid ester xe2x80x9cand the like.
The imaging medium of the present invention desirably comprises a binder, preferably a polymeric binder, which serves to bind the infrared dye and the photochemical acid progenitor into a coherent layer which can be handled easily.
Non-limiting examples of binders include polymers and copolymers of acrylic acid or esters thereof, methacrylic, acid or ester thereof, (anhydrous) maleic acid or esters thereof, acrylonitrile, styrene, xcex1-alkylstyrene, xcex1-acetoxystyrene, hydroxystyrene, xcex1-alkylhydroxystyrene, xcex1-acetoxyhydroxystyrene, or the substituted compounds obtained by protecting the hydroxy groups of the above compounds with a protecting group easily hydrolyzable by acid treatment (for example, trialkylsilyl group, tetrahydropyranyl group, t-butoxycarbonyl group and the like), or cyclic analogues thereof, vinyl acetate, vinyl chloride, vinylidene chloride, butadiene, crotonic acid, itaconic acid, N-substituted maleimide, vinyl benzoate, or copolymer of the above esters, polyethylene oxide, polyvinyl pyrrolidone, polyamide, polyurethane, polyethylene terephthalate, acetyl cellulose, methyl cellulose, ethyl cellulose, polyvinyl butyral, chlorinated polyolefin, polyalkylene, polyaldehyde, polycarbonate, epoxy resin, cresol novolak resin, resole resin, melamine resin, alkyl resin, modified polyvinyl alcohol, or block or graft copolymer or modified polymer by combination of them and the like. For applications such as positive acting printing plates, resists and proofs, binders which do not require a post exposure heating step before development will be preferred. Such binders include, for example, the homo- and copolymers of tetrahydropyranyl(meth)acrylate.
For improving the plasma-resistance upon development, a substituent containing silicone may be introduced in the binder before or after exposure to light.
Preferably, the proportion of the squarylium dye of formula (I) is 0.01 to 0.6 parts by weight (referred to as xe2x80x9cpartxe2x80x9d hereinafter) relative to-one part of acid progenitor, and preferably, the amount of the binder is 2 to 100 parts, and more preferably, 5 to 50 parts, relative to one part of the acid progenitor.
Though not wishing to be limited or restricted by any theory or mechanism for acid generation in the present invention, the process of acid formation from the combination of near infrared dyes of the present invention with acid progenitors may take place by one of several mechanisms. Efficient energy transfer from an excited state of a donor to a ground state receptor requires that the excited state energy of the donor is higher than the excited state energy of the receptor, as is well known in the art. Therefore, energy transfer from the irradiated excited state of the near infrared dye to the acid progenitor is unlikely due to the high singlet and triplet energies of the acid progenitors and the low excited state energies of the near-infrared dyes used in the present invention.
One method of introducing light energy in an imagewise fashion is the use of short pulses of high intensity laser light to excite the near infrared dyes of the present invention. The excited state of the irradiated near infrared dye can undergo radiationless transition back to the ground state of the dye resulting in light-to-heat conversion as is well known in the art. Depending on the fluence of the laser source, several hundreds of degrees centigrade can be achieved during the pulse or dwell time of the laser light. These high temperatures could then result in the thermal decomposition of the acid progenitors to produce acid. According to this mechanism, one might expect the sensitivity of the media of the present invention to be independent of the structure of the near infrared dyes used in the present invention since all of the dyes used in the present invention are capable of light-to-heat conversion. However, the sensitivities of the media used in the present invention are dependent on the dye structure. Although the light-to-heat conversion mechanism may still contribute to the generation of acid in the present invention, it does not appear to be the sole or dominant mechanism.
One possibility is that sensitization of acid progenitors by near-infrared dyes used in the present invention requires electron transfer from the excited state of the irradiated near-infrared dye to the acid progenitor. It is well known in the art that the efficiency of electron transfer depends strongly on the free energy change, xcex94G0, associated with photoinduced electron transfer, in this case from the excited state of the near-infrared dye to the acid progenitor. This free energy-change may be expressed by the Rehm-Weller relationship (D. Rehm and A. Weller, Isr. J. Chem., 1970, 8, 259) as follows:
xcex94G0=(Eoxsensxe2x88x92Eredinitxe2x88x92eo2/xcex5a)xe2x88x92E0,0sens
where Eoxsens and Eredinit are the ground state oxidation potential of the sensitizing near-infrared dye and reduction potential of the acid progenitor initiator, respectively, and E0,0sens is the excitation energy of the 0,0 band of the sensitizing near-infrared dye. According to the Rehi-Weller relationship, the efficiency of electron transfer increases as the oxidation potential of the sensitizing dye becomes less positive and the reduction potential of the acid progenitor initiator becomes less negative. Indeed the effectiveness of the near-infrared dyes used in the present invention in generating acid has been found to correlate with the oxidation potential of the near-infrared dye. Accordingly, it is preferred that the dye used in the present invention have an oxidation potential in dichloromethane not greater than about 0.8 V, and more preferably, not greater than about 0.7 V, relative to a standard calomel electrode when the acid progenitor is diaryliodonium salts, aryldiazonium salts, or 1,3,5-tris(trichloromethyl)-s-triazine. Dyes having oxidation potentials greater than about 0.8 V have been found not to be good sensitizers of acid progenitors, presumably because the high oxidation potential of the dye renders the free energy change xcex94Gxc2x0 for electron transfer between the excited state of the near-infrared dye and the acid progenitor unfavorable. Thexe2x80x9d preferred oxidation potential of near infrared dyes used in the present invention may vary, of course, for sensitization of acid progenitors of lower or higher reduction potential.
However, as the oxidation potential of the near infrared sensitizing dye becomes less positive and the reduction potential of the acid progenitor initiator becomes less negative, ground state electron transfer from the near infrared dye to the acid progenitor initiator becomes more favorable. Ground state electron transfer from the near infrared dye to the acid progenitor initiator can also lead to the formation of acid, which in turn can lead to instability of the imaging composition and shelf life problems which render the imaging composition useless. Therefore, as the oxidation potential of the sensitizing near-infrared dyes of the present invention becomes too low, shelf life problems may occur. Indeed the stability of the imaging compositions of the present invention have been found to correlate with the oxidation potential of the near-infrared dye. Accordingly, it is preferred that the dye used in the present invention has an oxidation potential in dichloromethane greater than about 0.55 V, and more preferably, greater than about 0.60 V, relative to a standard calomel electrode, if the acid progenitor is a diaryliodonium salt, aryldiazonium salt, or 1,3,5-tris(trichloromethyl)-s-triazine. The instability observed under accelerated aging conditions (3 days at 60xc2x0 C.) indicates that imaging media containing near infrared dyes used in this invention having oxidation potentials less than about 0.60 V would have limited utility when used with acid progenitors such as diaryliodonium salts, aryldiazonium salts, or 1,3,5-tris(trichloromethyl)-2,4,6-triazine.
Imaging compositions containing the near infrared dyes used in the present invention having oxidation potentials in the range of about 0.5 V to about 0.7 V have been found to have sufficient sensitivities to be useful in practice when the acid progenitor is diaryliodonium salts, aryldiazonium salts, or 1,3,5-tris(trichloromethyl)-s-triazine. Prior art near infrared dyes as disclosed in U.S. Pat. No. 5,401,607 were found not to be useful for sensitizing acid progenitors such as diaryliodonium salts when their oxidation potentials in dichloromethane were greater than about 0.5 V versus the standard calomel electrode.
A beneficial property of the near infrared dihydroperimidine squarylium dyes used in the present invention is their ability to achieve a wide range of oxidation potentials in the range of about 0.5 V to about 0.9 V by manipulation of the dihydroperimidine end group substituents. In this manner, the oxidation properties of the dye can be manipulated to give the best properties of sensitivity and shelf life in conjunction with the particular acid progenitor and imaging construction chosen.
Imaging compositions containing infrared dyes used in the present invention may be used to initiate any of the acid-dependent reactions initiated by prior art acid-generating reactions which produce an acid of comparable strength. Preferred acid-dependent reactions relate-to chemical amplification resist compositions of the negative and positive type which can be characterized by high sensitivity to visible and near infrared regions of the electromagnetic radiation spectrum. For example, the present process may be used to trigger an acid-catalyzed polymerization reaction, an acid-catalyzed crosslinking reaction, an acid-catalyzed depolymerization reaction, an acid-catalyzed de-protection reaction, or an acid-catalyzed destruction of dissolution inhibiting agent.
For example, a negative type resist using a thermal acid-catalyzed crosslinking reaction, represented by the acid-catalyzed crosslinking of phenolic resins by a crosslinking agent, is known (U.S. Pat. No. 5,368,783). Such resists may require a heat treating step following the light irradiation. In this case it is preferred that the development temperature is less than the decomposition temperature of the acid generating initiator.
Compounds which may be used as crosslinking agents include amino compounds having as functional groups at least two alkoxymethyl groups, methylol groups, or acetoxymethyl groups and the like. Examples include melamine derivatives (e.g., hexamethoxymethylated melamine, available from Mitsui-Cyanamid, Ltd. as CYMEL(copyright) 300 series (1) and the like); benzoguanamine derivatives (e.g., methylethyl mixed alkylated benzoguanamine resin, available from Mitsui-Cyanamid, Ltd. as CYMELO 1100 series (2)) and the like); and glycoluril derivatives (e.g., tetramethylolglycoluril, available from Mitsui-Cyanamid, Ltd. as CYMEL(copyright) 1100 series (3) and the like). Also included are di-substituted aromatic compounds having functional groups such, as alkoxymethyl groups, methylol groups, acetoxymethyl groups and the like. Examples of such compounds include 1,3,5-trihydroxymethylbenzene, 1,3,5-triacetoxymethylbenzene, 1,2,4,5-tetraacetoxymethylbenzene, and the like. These crosslinking agents can be synthesized according to the method described in Polym. Mater. Sci. Eng., 64, 241 (1991).
The amount of the crosslinking agent is preferably 0.1 to 100 parts, more preferably 0.2 to 50 parts, relative to one part of the photochemical acid generator.
Positive type resists based on acid-catalyzed de-protection reactions are known. For example, the de-protection of tetrahydropyran groups from derivatized polyacrylate and methacrylate polymers in which the exposed material becomes soluble in developer is disclosed in U.S. Pat. No. 5,102,771.
Positive type resists based on the acid-catalyzed destruction of a dissolution inhibiting agent in which the exposed material becomes soluble in developer are disclosed in European Patent Publ. No. 424,124 and U.S. Pat. No. 5,085,972. Such positive type resists consist of, for example, a novolak resin, a dissolution inhibiting agent such as the bis-tetrahydrofuranyl ether of bisphenol A, an acid progenitor such as a diaryliodonium salt, and a sensitizing dye for the acid progenitor.
Further, solvent (such as methylethylketone, 1-methoxy-2-propanol, ethyl cellosolve and the like), plasticizer (such as dioctyl phthalate and the like), dark reaction inhibitor, colorant composed of organic or inorganic dye or pigment and the like may be contained therein depending upon the use of the chemically amplifying resist.
A composition of the present invention is prepared, for example, by mixing the dye of formula (1), an acid progenitor, a binder and, if necessary, a crosslinking agent or dissolution inhibitor or the like. This composition may be coated by any method known in the art (e.g., knife coating, bar coating, curtain coating, etc.) on a substrate. The nature of the substrate is not critical and includes, for example, paper, plastic, glass, metal plates, etc. For example, a photosensitive material having high sensitivity to near infrared radiation can be prepared by coating a solution of the composition of the present invention dissolved in a solvent (such as methylethylketone and the like) on an aluminum plate having a treated surface, a silicon wafer, a glass plate, or a plastic film and the like, and drying.
In the practice of the present invention, light sources from the visible to near infrared are used to deliver an electromagnetic radiation pattern which can be absorbed by the dye of formula (I) in the imaging layers. Suitable light sources include mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, tungsten lamps, halogen lamps, flash lamps, light-emitting diodes, laser rays, semiconductor diode lasers, Ti-Sapphire lasers and the like.
It is advantageous to employ light sources which are relatively richer in near infrared wavelengths. Preferred non-laser light sources include high power (250 W to 10 kW) tungsten lamps and xenon lamps. When a laser is used it is preferred that it emit in the red or near infrared region of the electromagnetic spectrum, especially from about 700 to 1200 nm. Suitable laser sources in this region include Nd:YAG, Nd:YLF and semi-conductor lasers. The preferred lasers for use in this invention include high power single mode laser diodes, fiber-coupled laser diode arrays, and laser diode bars producing 0.1 to 12 W in the near infrared region of the electromagnetic spectrum.
The entire construction may be exposed at once, or by scanning, or with a pulsed source, or at successive times in arbitrary areas. Simultaneous multiple exposure devices may be used, including those in which the light energy is distributed using optical fibers, deformable micromirror arrays, light valves, and the like. Preferably, a solid state infrared laser or laser diode array is used. Sources of relatively low intensity are also useful, provided they are focused onto a relatively small area. If a non-laser light source is used, the entire construction may be exposed at once through an image mask, such as a graphic arts film mask or a chrome glass mask.
Exposure may be directed at the surface of the imaging layer containing the imaging materials of this invention, or through a transparent substrate beneath such an imaging layer. Exposure energies will depend on the type of sensitizer of compound (I), the type of photochemical acid generator, and the type of materials used in creating a negative or positive image. The rate of scanning during the exposure may also play a role. Exposure energies will be chosen so as to provide a degree of cure or reaction to be useful for the particular application. Laser exposure dwell times are preferably about, 0.05 to 50 microseconds and laser fluences are preferably about 0.001 to 1 J/cm2. Non-laser exposure dwell times are preferably about 5 seconds to about 10 minutes and fluences are preferably about 0.01 to 1 J/cm2.
The following non-limiting examples further illustrate the present invention.